I’m looking at the digital speedometer as it passes 200km/h and I can still feel the rear end squirming

The name sums up the car. The name is meant to be said as 'one-to-one', as an expression of its perfectly balanced power-to-weight ratio of one metric horsepower to one kilogram of mass (or 986bhp per tonne).

That’s when the twin-turbocharged 5.0-litre V8 engine is running on its favoured diet of E85 Ethanol, which is freely available in Sweden. Running on regular super-unleaded – as we are today - the output is restricted to just 1160bhp, although that’s still good for 852bhp per tonne.

It’s still raining and on the sodden surface of the runway something close to open warfare breaks out between the One:1’s engine and its stability control system, the engine fluttering as the vast 345/30 R20 Michelin Sport Pilots struggle for grip at the back. It never arrives: I’m looking at the digital speedometer as it passes 200km/h and I can still feel the rear end squirming.

And then, with jarring suddenness, the runway is approaching sideways and the driver is frantically winding on opposite lock. For a second or so he holds the slide, but then there’s the sensation of the pendulum swinging the other way and the One:1 starts to spin towards the rushing green that edges the asphalt. Fortunately we encounter nothing more than wet grass as we scythe a 50-yard track off the runway and stop, the cabin filled with nervous laughter.

The car itself is blameless. Walking back to where the spin started reveals deeply pooled water across the runway; even all that downforce couldn’t stop us from aquaplaning.

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My turn to drive, and my pulse is racing even before starting the engine. The driving position is intimate, sitting in tight-fitting seats and with pretty much every surface made from either carbonfibre or covered in Alcantara. Three VDU instruments sit behind the steering wheel, with the temperature display incorporating a ‘power’ gauge in PS that reads to 1500. The speedo goes to 450km/h. Neither is exaggerating.

The automated gearbox has a single ‘drive’ clutch and a second that acts as a brake to cut the time of high-speed upchanges, but at trundling pace there’s a hesitation between ratios and a forceful clunk as the next one slots in.

But nothing is going to change the immutable laws of physics, specifically the lack of friction between the tyres and the runway’s slick surface. An experimental prod of the throttle at around 60mph in third gear produces a stab of acceleration and then, as the turbos spool up, the back end starts to struggle for grip.

The stability control works well to keep everything straight, but I know I’m only experiencing a scant percentage of the One:1’s performance. Pushing the throttle down further produces a Götterdämmerung of noise and fury from behind the cockpit. The acceleration feels immense, yet throughout this the power gauge doesn’t rise above 600PS; I’m experiencing less than half what the car has to offer.

We give up on the runway and move onto some of the local roads. Considering it’s the turned-up-to-11 version of what is already a track-focussed car, the One:1 copes well with the real world, even on the narrow roads of this part of the world.

The good news is that we’ve got the following morning with the car as well. It dawns grey and overcast, but the rain has stopped – and back at the runway the standing water has gone, although the surface is still cold and greasy.

After a gentle rolling start I floor the throttle as I select second gear. The back end is still squirming as the torque arrives, but the juddering of the previous day is gone and the response is far stronger. Through third and into fourth the engine is still flaring as the stability control cuts in.

Sorry, even if you have the wherewithal to buy one, you can’t – Koenigsegg has already sold the seven it will produce (a figure that includes the prototype that we drove).

If you’re tempted, and you can swing the seven-figure pricetag, then you can still buy the less powerful but equally track-focussed Koenigsegg Agera RS, or put your name down for the forthcoming hybrid Regera, a car Koenigsegg claims will be even faster.

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